1. Technical Field
The present invention pertains to air separation units combined with oxygen fired power generation systems.
2. Discussion of the Related Art
Cryogenic air separation is typically preferred in the industry for yielding large volumes of oxygen and nitrogen, which may then be used in variety of different power generation systems. However, a drawback to a cryogenic air separation system is that power costs associated with system operation can run as high as 50% of the overall operational costs, where most of the power is consumed by the main air compressor disposed upstream of the air separation unit. Accordingly, the power costs associated with the main air compressor have a strong influence on the total production cost of the products emerging from the air separation unit. Optimization of the turbine configuration that drives the main air compressor is desirable in order to reduce power costs associated with system operation.
A variety of different systems are known in the art that integrate air separation units with power generation processes in one form or another. For example, U.S. Pat. No. 6,282,901 to Marin et al. describes an integrated air separation process that produces an oxygen enriched gas stream and a nitrogen enriched gas stream. The nitrogen enriched gas stream is heated in a first heat exchanger associated with a first boiler and then used to generate power. The oxygen enriched gas stream is introduced with fuel to a combustor associated with the first boiler to produce a flue gas, and at least a portion of the flue gas exiting the boiler is used to generate power.
U.S. Pat. Nos. 6,202,442 and 6,276,171 to Brugerolle describe integrated power generation systems where part of the air emerging from a gas turbine compressor is sent to an air separation unit and another part is sent to a combustor of the gas turbine. A nitrogen gas stream emerging from the air separation unit is mixed with the discharge of the gas turbine combustor and then sent to the gas turbine expander. The Brugerolle systems generate power and also produce an oxygen-enriched fluid.
U.S. Pat. No. 4,785,622 to Plumley et al. describes an integrated coal gasification plant and combined cycle system employing a supply of compressed air bled off from an air compressor portion of a gas turbine to supply the compressed-air needs of an oxygen plant associated with the coal gasification plant. The high temperature exhaust from the turbine section of the gas turbine is utilized to generate steam, and the generated steam is delivered to a steam turbine to generate a mechanical output in addition to the output generated by the gas turbine. In order to compensate for the removal of compressed air fed to the oxygen plant, the spent steam from the steam turbine is added to the compressed air and fuel fed to the combustor portion of the gas turbine. The system of Plumley et al. eliminates the need for a separate compressor to provide compressed air to the oxygen plant.
U.S. Pat. No. 6,148,602 to Demetri describes a solid-fueled power generation system with carbon dioxide sequestration including an air compressor and an oxygen compressor driven by a single gas turbine. The air compressor delivers compressed air to an air separator, with substantially pure oxygen emerging from the air separator being further compressed by the oxygen compressor and then divided into two streams. The first stream is delivered to a gasifier and the second stream to a combustor for the gas turbine. The first stream is combined with a solid fuel in the gasifier and converted into a combustible gas that is sent to the combustor. Water is also injected into the combustor, and an exhaust stream of carbon dioxide and steam emerging from the combustor is passed into the gas turbine for driving the turbine and providing power.
A system described by Bolland et al. (Energy Conversion & Mgmt, Volume 33, No. 5-8, 1992, pages 467-475) includes a combustor that receives oxygen from an air separation plant and reacts the oxygen with a fuel gas, followed by delivering the combustion products to a turbine. A water stream is passed through a heat exchanger to cool compressed air discharged from an air compressor before the compressed air is directed to the air separation plant, and the water or steam discharge from the heat exchanger is then delivered to the combustor to cool the combustor products down to a permissible turbine inlet temperature.
A GOOSTWEG power plant, which is described by Yantovskii (World Clean Energy Conference, Geneva, Switzerland, November 1991, pages 571-595), includes a first combustion chamber that receives oxygen from an air splitting machine, a hydrocarbon fuel and water to produce a drive gas of carbon dioxide and steam that is delivered to a high pressure turbine. The discharge from the high pressure turbine is reheated in a second combustion chamber and delivered to a medium pressure turbine, followed by a reheating in a third combustion chamber and delivery to a low pressure turbine. Carbon dioxide is separated from water in a degasser, and the separated water is then heated and recycled back to the first combustion chamber.
While each of the systems described above provides certain efficiencies and advantages, there still exists a need to provide an integrated air separation and power generation system with an optimized configuration to reduce power requirements and thus operating costs associated with operation of the air separation unit.